Sodium arsenite, a major form of environmental arsenic, cross-links vicinyl protein sulfhydryl groups, leading to multiple toxic cellular responses, including oxidative stress. We found that arsenite, even at low concentrations, substantially inhibits adrenal steroid production both in rats in vivo and in cultured cells. The key step in the regulation of steroidogenesis by cAMP is the transfer of cholesterol by cAMP is the transfer of cholesterol to the inner mitochondrial cytochrome P450/SCC. The Steroidogenic Acute Regulatory protein (StAR) plays a major role in this process. This protein is formed as a 37 kDa precursor that is phosphorylated by protein kinase A (PKA) and is processed to more active 30 kDa in the mitochondria. This processing is coupled to enhanced cholesterol transport from the outer to the inner mitochondrial membrane. This continuous translation and processing is necessary for cholesterol transfer. We will show that arsenite suppresses cholesterol metabolism in adrenal (primary and Y-1) and testis Leydig (MA-10) cells, while also attenuating this essential StAR processing. Arsenite, at very low concentrations, substantially potentiates cAMP-induced StAR transcription prior to suppression at higher concentrations. Another oxidative stress agent, anisomycin, shows a similar biphasic effect on this process and, like arsenite, activates stress-activated protein kinases (SAPK), such as JNK and p38. We propose that SAPK stimulation of StAR transcription provides a protective mechanism to sustain StAR activity as later key steps are inhibited. We will establish, with selective inhibitors that arsenite alters the transcription and the stability of StAR mRNA primarily via the activation of p38. The transcriptional modulation involving arsenite will be analyzed by dissecting the StAR upstream regulatory region, particularly sites recognizing the SF-1 nuclear regulator. Arsenite modulation of the activity of normal and mutated recombinant SF-1 on StAR-luciferase reporters will be used to further define the mechanism. The proposed research will provide mechanistic insight into a novel adrenal response to chemical stress that may be shared by other steroidogenic cells. Effects of arsenite on SF-1 regulation have broader relevance to adrenal/gonadal development regulated by this factor.